1. Field of the Invention
The present invention relates to an electric circuit having an electronic function memory for maintaining the functional state of an electrical system of a motor vehicle during a power failure or interruption.
2. Background Art
These types of circuit arrangements are provided in order to permanently maintain an electrical system provided with two different function states. Thus, for example, it is possible in that the system is directly allocated to a power switch device. The power switch device includes a latching position which can be reached from a neutral position in order to realize one of each of two respective function states.
In the course of further development, the power-transmitting and consequently also the switching devices are replaced by push-button operatedxe2x80x94only control currents conductingxe2x80x94switching devices, such as silicon switching mats, which, for example, are then allocated to bi-stable power switching relays. Embodiments of this type, however, require quite a considerable expenditure, both in terms of material and related space.
Further, it is known that, apart from these electromechanical solutions, an electronic storage operation of the respective function state must be effected. For this, a prior art specific bi-stable flip-flop may be used for storing a digital state. The flip-flop can be realized by varying technologies, such as CMOS. Such developed electronic function memories have a common characteristic in that the stored state is lost as soon as the supply of voltage of the circuit arrangement is no longer supplied. Providing an emergency power supply in the form of a storage battery or a high-capacity capacitor involves increased expenditure and only offers conditional long-term stability.
Further, for example, it is known from U.S. Pat. No. 4,388,704 to provide a bi-stable flip-flop with a device by means of which the current digital state of the flip-flop is maintained even if the supply voltage is interrupted. This type of embodiment, however, is not suitable for electrical systems installed in motor vehicles, which are operated by push-button switching devices.
Further, it is known from RELAIS LEXIKON, 2nd edition, Dr. Alfred Hxc3xcthig Verlag, Heidelberg 1985, pp. 62 and 226-242, to combine switching modules with integrated circuits, which are considered as control stages, so that a multitude of switching tasks in connection with a power switching stage can be realized by simple means. This also includes a circuit arrangement with a conventional flip-flop, which is influenced by pulse-shaped signals. The pulse-shaped signals may also be generated by push-buttons.
Further, Halbleiter-Schaltungstechnik [Semiconductor Circuit Technology], by Tietze, Schenk et al., Springer Verlag 1999, pp. 751-752, describes electrically erasable read-only memories, i.e., EEPROMs.
In addition, an electrical circuit arrangement with switching devices for initiating various functions is known from DE 198 45 135 A1, in which a control stage existing therein is a memory module developed as an EEPROM. An allocation table is stored in the memory module which allocates to each individual switching device functions which are to be influenced by the respective switching device and/or by the control stage out of a number of functions.
Finally, from JP 09 298020 A, an electrical circuit device is known for controlling a water preparation system. The electrical circuit device includes several control stages in which a key operated switching element having a switching device is allocated to each control stage. The switching state of each control stage is stored by a flip-flop formed of a EEPROM cell in a respective integrated switching module. With this embodiment, however, each control stage is provided with a microcomputer and is connected via two signal outputs and a two-wire data bus line with the electronic system. This represents a considerable expenditure.
From the above-mentioned background art there is indeed no indication in the synopsis of existing circumstances to develop and design a non-volatile flip-flop from a few EEPROM cells, i.e., to integrate the flip-flop in the control stage so that the pertinent system alone is to be influenced via a signal output of the control stage and, thus, via merely one electrical connecting line.
In view of the foregoing, it is an object of the present invention to provide an electric circuit arrangement having an electronic function memory, which is suitable for motor vehicle electrical systems, in which in the case of external and internal power failures or interruptions the previously existing function state is maintained for almost any period of time. With this type of design of an electric circuit arrangement, it is advantageous that the system can be realized with relatively simple means, in which the means only have minimal space requirements, as only one electrical connecting line is needed to connect the signal output of the control stage to the motor vehicle electrical system.
In carrying out the above object and other objects, the present invention provides an electric circuit for an electrical system in a motor vehicle. The electrical system is powered by a voltage supply and has two functional states. The electric circuit includes a control stage having a switching device, an electronic switching module, a single signal output, and a single connecting line connecting the signal output to the electrical system.
The switching device includes at least one manually operated push-button switching element switchable between two switching states for generating respective switching state output signals at the signal output in order to switch the electrical system between the two functional states. The electronic switching module includes a non-volatile flip-flop formed by EEPROM cells which are operable for storing the switching state of the switching element. The electronic switching module maintains the switching state output signal corresponding to the stored switching state at the signal output to maintain the functional state of the electrical system until the switching element is switched to a different switching state. The electronic switching module maintains the switching state output signal corresponding to the stored switching state at the signal output to maintain the functional state of the electrical system during an interruption of power from the voltage supply to the electrical system.
The flip-flop preferably includes an odd number of EEPROM cells, such as three EEPROM cells. The electronic switching module may further include an evaluation stage operable for scanning respective states of the EEPROM cells of the flip-flop. The evaluation stage includes a test component and a control logic. The control logic includes a probability component. The test component is operable for checking the respective states of the EEPROM cells and influences the control logic if the respective states of the EEPROM cells are identical. The probability component exercises a corresponding influence if the respective states of the EEPROM cells are not identical.
The at least one manually operated push-button switching element may include two manually operated push-button switching elements switchable between two switching states for generating respective switching state output signals at the signal output in order to switch the electrical system between the two functional states. The electronic switching module includes first and second inputs which are connected to the voltage supply. The two switching elements are connected between respective inputs of the electronic switching module and the voltage supply such that operation of the first switching element causes the switching state output signal xe2x80x9c0xe2x80x9d at the signal output and operation of the second switching element causes the switching state output signal xe2x80x9c1xe2x80x9d at the signal output. The electronic switching module may further include a pair of light-emitting diodes each inserted respectively between the first and second inputs of the electronic switching module and the voltage supply in series with the respective switching elements. The light-emitting diodes emit light when their respective switching element is operated. The two light-emitting diodes emit different colored light such as red and green light.
A positive pole of the voltage supply is connected to an external voltage input of the electronic switching module via a limiting resistor which limits the transformed dissipation loss in the case of over-voltage. An external supply input of the electronic switching module is connected to an internal supply input via an integrated diode which provides polarity reversal protection. A support capacitor is connected between the internal supply input and a grounded terminal of the electronic switching module to stabilize the voltage supplied by the voltage supply to the electronic switching module.